This proposal will optimize 2 approaches to suppress established IgE-mediated allergy, test these approaches in a mouse model of food allergy and determine how they work. Food allergy affects 2-4% of adults and is responsible for ~30,000 emergency room visits/year in the U.S. Our VA-sponsored, mouse model studies have better defined the mechanisms responsible for food allergy and discovered approaches that can suppress established disease. Achievements include demonstrations that: 1) ingested antigen must be absorbed systemically (where it can be neutralized by IgG antibodies) to induce anaphylaxis; 2) a monoclonal antibody (mAb) to the IgE binding chain of the high affinity IgE receptor, Fc5RI1, can induce anaphylaxis, which can be prevented by a rapid desensitization approach and by pre-treatment with corticosteroids plus antihistamine; 3) anti-Fc5RI1 mAb treatment can suppress established food allergy; and 4) addition of a single dose of anti-CD4 mAb considerably enhances anti-Fc5RI1 mAb suppression of established food allergy. In addition we have developed a mouse model of anaphylaxis that utilizes IgE antibodies from human allergy patients. We will now build on these achievements by better defining the mechanisms responsible for our observations and optimizing our approaches for suppression of established food allergy. This should set the stage for applying these approaches to food-allergic humans. First, we will test the hypothesis that effects of the cytokines IL-4 and IL-13 on non-bone marrow derived cells, such as vascular endothelial cells, smooth muscle cells, and intestinal epithelial cells, are critical during the effector phase of food allergy. We will use mAbs, bone marrow IL-4 receptor 1 chain (IL-4R1) chimeric mice and mice that have deleted from specific cell types to evaluate: a) whether systemic shock and allergic diarrhea can be suppressed by treating mice with anti-IL-4R1 mAb once food allergy has become established; b) whether mice that lack IL-4 receptors on non-bone marrow-derived cells develop food-induced anaphylaxis normally; and c) whether mice that selectively lack IL-4R1 on smooth muscle cells, intestinal epithelial cells, and/or vascular endothelial cells develop food-induced anaphylaxis normally. Next, we will determine how the combination of anti-Fc5RI1 mAb and anti-CD4 mAb suppresses established food allergy and will optimize suppression of food allergy by combined mAb treatment. Although the synergistic suppression of severe, established food allergy by the combination of these two mAb results, in part, from prevention of development of anti-hamster IgG antibodies that neutralize the hamster anti-mouse Fc5RI1 mAb, the combination of anti-Fc5RI1 mAb and anti-CD4 mAb also suppresses food allergy better than anti-Fc5RI1 mAb alone prior to the development of neutralizing anti-hamster IgG antibody. We will use in vitro and in vivo experiments to determine: a) whether enhancement of anti-Fc5RI1 mAb suppression of established food allergy by anti-CD4 mAb coincides with enhanced suppression of the IL-4 and IL-13 responses to Ag challenge, enhanced suppression of mast cell degranulation, or both; b) the extent of CD4+ T cell inhibition required to enhance anti-Fc5RI1 mAb suppression of established food allergy; c) whether an anti-Fc5RI1 mAb that is not seen as foreign can completely suppress severe established food allergy in the absence of anti-CD4 mAb; and d) how the combination of anti-Fc5RI1 mAb plus anti-CD4 mAb induces long-lasting suppression of established food allergy. Our third aim will determine whether the combination of systemic immunization and IL-4R1 blockade synergistically suppresses established food allergy. Because IgG antibodies can suppress established food allergy and anti-IL-4R1 mAb can suppress IgE responses without suppressing IgG responses, we hypothesize that combining anti-IL-4R1 mAb treatment with allergen immunization will potently suppress established food allergy. Taken together, these proposed studies should provide powerful new approaches for the suppression of food allergy and other IgE-mediated disease and, by determining how these approaches work, identify ways to improve them further.